This invention relates generally to the reduction or elimination of mechanical vibrations, particularly in a coupled pair that comprises a Stirling cycle machine that is drivingly linked to an electromagnetic linear motor or alternator and more particularly relates to the reduction or elimination of mechanical vibration at harmonics of the fundamental operating frequency of reciprocation of the coupled pair through integration of the control system of the invention with prior art controls and vibration balancers.
Many machines vibrate as a consequence of the repetitive acceleration and deceleration of one or more periodically moving masses that are a part of the machine. In some environments the vibrations can be uncomfortable, distracting or annoying and in some they can interfere with the operation of other equipment and can even result in damage. One manner of reducing vibration is to mount the vibrating machine to another mass through an intermediate vibration damper, which may be a device or material that absorbs some of the energy of the vibration. However, because that way can only partially reduce the vibrations, a more effective way to eliminate, or at least minimize, the amplitude of the vibrations is to rigidly mount a vibration balancer to the vibrating machine. A vibration balancer generates forces that oppose the vibration; that is, it generates forces that are equal or nearly equal in amplitude but opposite in phase to, and thereby cancel or nearly cancel, the forces produced by the vibration.
Vibration balancers are generally of two types, passive vibration balancers and active vibration balancers, some of which are also known as tuned mass dampers, active mass dampers or vibration absorbers. A passive vibration balancer is essentially a resonant spring and mass system that is tuned to the operating frequency of the vibrating machine but is arranged to apply the forces from its accelerating and decelerating mass to the vibrating machine at a phase that is 180° out of phase with the forces resulting from the vibration. An active vibration balancer is essentially a mass, and may also be linked to a spring, but the motion of the mass is controlled by a feedback control system that senses the vibrations and drives the mass in opposition to the vibrations.
Although a passive balancer is less expensive, it has the disadvantage that it can only respond to vibrations at the one resonant frequency to which it is tuned. An active balancer can respond to small variations in the frequency of the vibrations and can apply a compensating force at an amplitude that better cancels the vibration but an active balancer is more expensive and requires a controller to drive the active balancer at the required amplitude and phase. As far as known to me, neither a passive nor an active balancer has balanced vibrations at harmonics of the fundamental operating frequency of a vibrating machine.
Therefore, it is an object and feature of the invention to provide a method and apparatus for diminishing or eliminating the vibrations of a machine at harmonics of the fundamental operating frequency of the machine.
A further object and feature of the invention is to not only balance the vibrations at harmonics of the fundamental operating frequency of the machine, but to do so without the addition of any mechanical structures for accomplishing that balancing.